Functional redundancy of the nuclear factor kappa B inhibitors I kappa B alpha and I kappa B beta

The molecular mechanism of NF-κB dysregulation across different subtypes of renal cell carcinoma

BACKGROUND

The nuclear factor kappa B (NF-κB) is a critical pathway that regulates various cellular functions, including immune response, proliferation, growth, and apoptosis. Furthermore, this pathway is tightly regulated to ensure stability in the presence of immunogenic triggers or genotoxic stimuli. The lack of control of the NF-κB pathway can lead to the initiation of different diseases, mainly autoimmune diseases and cancer, including Renal cell carcinoma (RCC). RCC is the most common type of kidney cancer and is characterized by complex genetic composition and elusive molecular mechanisms.

AIM OF REVIEW

The current review summarizes the mechanism of NF-κB dysregulation in different subtypes of RCC and its impact on pathogenesis.

KEY SCIENTIFIC CONCEPT OF REVIEW

This review highlights the prominent role of NF-κB in RCC development and progression by driving the expression of multiple genes and interplaying with different pathways, including the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. In silico analysis of RCC cohorts and molecular studies have revealed that multiple NF-κB members and target genes are dysregulated. The dysregulation includes receptors such as TLR2, signal-transmitting members including RelA, and target genes, for instance, HIF-1α. The lack of effective regulatory mechanisms results in a constitutively active NF-κB pathway, which promotes cancer growth, migration, and survival. In this review, we comprehensively summarize the role of dysregulated NF-κB-related genes in the most common subtypes of RCC, including clear cell RCC (ccRCC), chromophobe RCC (chRCC), and papillary RCC (PRCC).

Molecular Mechanisms Underlying the Anti-Inflammatory Properties of (R)-(-)-Carvone: Potential Roles of JNK1, Nrf2 and NF-κB

To explore the molecular mechanisms underlying the anti-inflammatory activity of (R)-(-)-carvone, we evaluated its ability to inhibit the signaling pathways involving the mitogen-activated protein kinases (MAPKs) and the transcription factor, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). (R)-(-)-carvone significantly decreased c-Jun N-terminal kinase (JNK) 1phosphorylation, but not that of the other MAPKs, induced by bacterial lipopolysaccharides (LPS) in the RAW 264.7 macrophage cell line. Although (R)-(-)-carvone significantly inhibited resynthesis of the inhibitor of NF-κB (IκB)-α induced by LPS, it did not interfere with the canonical NF-κB activation pathway, suggesting that it may interfere with its transcriptional activity. (R)-(-)-carvone also showed a tendency to decrease the levels of acetylated NF-κB/p65 in the nucleus, without affecting the activity and protein levels of Sirtuin-1, the major NF-κB/p65 deacetylating enzyme. Interestingly, the nuclear protein levels of the transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and the expression of its target,, heme oxygenase-1 (HO-1), an antioxidant enzyme, also showed a tendency to increase in the presence of (R)-(-)-carvone. Taken together, these results suggest that the ability of (R)-(-)-carvone to inhibit JNK1 and to activate Nrf2 can underlie its capacity to inhibit the transcriptional activity of NF-κB and the expression of its target genes. This study highlights the diversity of molecular mechanisms that can be involved in the anti-inflammatory activity of monoterpenes.

APAP-induced IκBβ/NFκB signaling drives hepatic IL6 expression and associated sinusoidal dilation

Acetaminophen (APAP) overdose results in high morbidity and mortality, with limited treatment options. Increased understanding of the cellular signaling pathways activated in response to toxic APAP exposure is needed to provide insight into novel therapeutic strategies. Toxic APAP exposure induces hepatic nuclear factor kappa B (NFκB) activation. NFκB signaling has been identified to mediate the pro-inflammatory response, but also induces a pro-survival and regenerative response. It is currently unknown whether potentiating NFkB activation would be injurious or advantageous after APAP overdose. The NFκB inhibitory protein beta (IκBβ) dictates the duration and degree of the NFκB response following exposure to oxidative injuries. Thus, we sought to determine whether IκBβ/NFκB signaling contributes to APAP-induced hepatic injury. At late time points (24 hours) following toxic APAP exposures, mice expressing only IκBβ (AKBI mice) exhibited increased serologic evidence of hepatic injury. This corresponded with increased histologic injury, specifically related to sinusoidal dilatation. Compared to wild-type (WT) mice, AKBI mice demonstrated sustained hepatic nuclear translocation of the NFκB subunits p65 and p50, and enhanced NFκB target gene expression. This included increased expression of interleukin-6 (Il-6), a known contributor to hepatic sinusoidal dilation. This transcriptional response corresponded with increased plasma protein content of Il-6, as well as increased activation of signal transducer and activator of transcription 3 (STAT3). Impact Statement: IκBβ/NFκB signaling is associated with a pro-inflammatory response, exacerbated Il-6 and STAT3 activation, and this was associated with late development of sinusoidal dilatation. Thus, targeting sustained IκBβ/NFκB signaling may represent a novel therapeutic approach to attenuate late hepatic injury following toxic APAP exposure.

Defining the structure of the NF-ĸB pathway in human immune cells using quantitative proteomic data

The NF-ĸB transcription factor is a critical regulator of immune homeostasis and inflammatory responses and is a critical factor in the pathogenesis of inflammatory disease. The pathways to NF-ĸB activation are paradigms for signal-induced ubiquitination and proteasomal degradation, control of transcription factor function by subcellular localisation, and the control of gene transcription and physiological processes by signal transduction mechanisms. Despite the importance of NF-ĸB in disease, the NF-ĸB pathway remains unexploited for the treatment of inflammatory disease. Our understanding of NF-ĸB comes mostly from studies of transgenic mice and cell lines where components of the pathway have been deleted or over expressed. Recent advances in quantitative proteomics offer new opportunities to understand the NF-ĸB pathway using the absolute abundance of individual pathway components. We have analysed available quantitative proteomic datasets to establish the structure of the NF-ĸB pathway in human immune cells under both steady state and activated conditions. This reveals a conserved NF-κB pathway structure across different immune cell lineages and identifies important differences to the current model of the NF-ĸB pathway. These include the findings that the IKK complex in most cells is likely to consist predominantly of IKKβ homodimers, that the relative abundancies of IκB proteins show strong cell type variation, and that the components of the non-canonical NF-ĸB pathway are significantly increased in activated immune cells. These findings challenge aspects of our current view of the NF-κB pathway and identify outstanding questions important for defining the role of key components in regulating inflammation and immunity.

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Quantitative proteomic datasets offer new insights into the NF-κB pathway.

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The structure of the NF-κB pathway is highly conserved in human immune cells.

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The IKK complex is likely composed mainly of IKKβ homodimers.

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The relative abundancies of IκBα, −β and -ε show strong cell type variation.

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Components of the non-canonical NF-ĸB pathway are greatly increased by activation.

MEST promotes lung cancer invasion and metastasis by interacting with VCP to activate NF-κB signaling

Background

Cell invasion is a hallmark of metastatic cancer, leading to unfavorable clinical outcomes. In this study, we established two highly invasive lung cancer cell models (A549-i8 and H1299-i8) and identified mesoderm-specific transcript (MEST) as a novel invasive regulator of lung cancer. We aim to characterize its biological function and clinical significance in lung cancer metastasis.

Methods

Transwell invasion assay was performed to establish high-invasive lung cancer cell model. Immunohistochemistry (IHC) was used to detect MEST expression in tumor tissues. Mass spectrometry and bioinformatic analyses were used to identify MEST-regulated proteins and binding partners. Co-immunoprecipitation assay was performed to detect the interaction of MEST and VCP. The biological functions of MEST were investigated in vitro and in vivo. Immunofluorescence staining was conducted to explore the colocalization of MEST and VCP.

Results

MEST overexpression promoted metastasis of lung cancer cells in vivo and in vitro by activating NF-κB signaling. MEST increased the interaction between VCP and IκBα, which accelerated IκBα degradation and NF-κB activation. Such acceleration was abrogated by VCP silencing, indicating that MEST is an upstream activator of the VCP/IκBα/NF-κB signaling pathway. Furthermore, high expressions of MEST and VCP were associated with poor survival of lung cancer patients.

Conclusion

Collectively, these results demonstrate that MEST plays an important role in driving invasion and metastasis of lung cancer by interacting with VCP to coordinate the IκBα/NF-κB pathway. Targeting the MEST/VCP/IκBα/NF-κB signaling pathway may be a promising strategy to treat lung cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02107-1.

Inhibitory feedback control of NF-κB signalling in health and disease

Cells must adapt to changes in their environment to maintain cell, tissue and organismal integrity in the face of mechanical, chemical or microbiological stress. Nuclear factor-κB (NF-κB) is one of the most important transcription factors that controls inducible gene expression as cells attempt to restore homeostasis. It plays critical roles in the immune system, from acute inflammation to the development of secondary lymphoid organs, and also has roles in cell survival, proliferation and differentiation. Given its role in such critical processes, NF-κB signalling must be subject to strict spatiotemporal control to ensure measured and context-specific cellular responses. Indeed, deregulation of NF-κB signalling can result in debilitating and even lethal inflammation and also underpins some forms of cancer. In this review, we describe the homeostatic feedback mechanisms that limit and ‘re-set’ inducible activation of NF-κB. We first describe the key components of the signalling pathways leading to activation of NF-κB, including the prominent role of protein phosphorylation and protein ubiquitylation, before briefly introducing the key features of feedback control mechanisms. We then describe the array of negative feedback loops targeting different components of the NF-κB signalling cascade including controls at the receptor level, post-receptor signalosome complexes, direct regulation of the critical ‘inhibitor of κB kinases’ (IKKs) and inhibitory feedforward regulation of NF-κB-dependent transcriptional responses. We also review post-transcriptional feedback controls affecting RNA stability and translation. Finally, we describe the deregulation of these feedback controls in human disease and consider how feedback may be a challenge to the efficacy of inhibitors.

Elucidation of the Mechanism Underlying the Anti-Inflammatory Properties of (S)-(+)-Carvone Identifies a Novel Class of Sirtuin-1 Activators in a Murine Macrophage Cell Line

The signaling pathways involved in age-related inflammation are increasingly recognized as targets for the development of preventive and therapeutic strategies. Our previous study elucidated the structure-activity relationship of monoterpene compounds derived from p-menthane as potential anti-inflammatory drugs and identified (S)-(+)-carvone as the most potent among the compounds tested. This study aims at identifying the molecular mechanism underlying the anti-inflammatory properties of (S)-(+)-carvone. The murine macrophage cell line, Raw 264.7, was stimulated with bacterial lipopolysaccharide (LPS) to simulate inflammation. Western blot was used to assess protein levels and post-translational modifications. The subcellular localization of NF-κB/p65 was visualized by immunocytochemistry. An in vitro fluorometric assay was used to measure Sirtuin-1 (SIRT1) activity. (S)-(+)-carvone inhibited LPS-induced JNK1 phosphorylation, but not that of p38 and ERK1/2 and also did not affect the phosphorylation and degradation of the NF-κB inhibitor, IκB-α. Accordingly, (S)-(+)-carvone did not affect LPS-induced phosphorylation of NF-κB/p65 on Ser536 and its nuclear translocation, but it significantly decreased LPS-induced IκB-α resynthesis, a NF-κB-dependent process, and NF-κB/p65 acetylation on lysine (Lys) 310. Deacetylation of that Lys residue is dependent on the activity of SIRT1, which was found to be increased by (S)-(+)-carvone, while its protein levels were unaffected. Taken together, these results show that (S)-(+)-carvone is a new SIRT1 activator with the potential to counteract the chronic low-grade inflammation characteristic of age-related diseases.

Control of Murine Primordial Follicle Growth Activation by IκB/NFκB Signaling

The transcription factor NFκB has been associated with the timing of menopause in a large human genome-wide association study. Furthermore, preclinical studies demonstrate that loss of Tumor necrosis factor alpha (Tnfα) or its receptor Tnfr2 slows primordial follicle growth activation (PFGA). Although Tnfα:receptor signaling stimulates NFκB and may mechanistically link these findings, very little is known about NFκB signaling in PFGA. Because signaling downstream of Tnfα/Tnfr2 ligand/receptor interaction has not been interrogated as relates to PFGA, we evaluated the expression of key NFκB signaling proteins in primordial and growing follicles, as well as during ovarian aging. We show that key members of the NFκB pathway, including subunits, activating kinases, and inhibitory proteins, are expressed in the murine ovary. Furthermore, the subunits p65 and p50, and the cytosolic inhibitory proteins IκBα and IκBβ, are present in ovarian follicles, including at the primordial stage. Finally, we assessed PFGA in genetically modified mice (AKBI) previously demonstrated to be resistant to inflammatory stress-induced NFκB activation due to overexpression of the NFκB inhibitory protein IκBβ. Consistent with the hypothesis that NFκB plays a key role in PFGA, AKBI mice exhibit slower PGFA than wild-type (WT) controls, and their ovaries contain nearly twice the number of primordial follicles as WT both at early and late reproductive ages. These data provide mechanistic insight on the control of PFGA and suggest that targeting NFκB at the level of IκB proteins may be a tractable route to slowing the rate of PFGA in women faced with early ovarian demise.

Inhibition of IκBβ/NFκB signaling prevents LPS-induced IL1β expression without increasing apoptosis in the developing mouse lung

BackgroundThe pro-inflammatory consequences of IL1β expression contribute to the pathogenesis of bronchopulmonary dysplasia. Selectively targeting Lipopolysaccharide (LPS)-induced IκBβ/NFκB signaling attenuates IL1β mRNA expression in macrophages. Whether targeting IκBβ/NFκB signaling affects the anti-apoptotic gene expression, a known consequence of global LPS-induced NFκB inhibition, is unknown.MethodsMacrophages (RAW 264.7, bone marrow-derived macrophage) were assessed for LPS-induced IL1β mRNA/protein expression, anti-apoptotic gene expression, cell viability (trypan blue exclusion), and activation of apoptosis (caspase-3 and PARP cleavage) following pharmacologic and genetic attenuation of IκBβ/NFκB signaling. Expressions of IL1β and anti-apoptotic genes were assessed in endotoxemic newborn mice (P0) with intact (WT), absent (IκBβ KO), and attenuated (IκBβ overexpressing) IκBβ/NFκB signaling.ResultsIn cultured macrophages, pharmacologic and genetic inhibition of LPS-induced IκBβ/NFκB signaling significantly attenuated IL1β mRNA and protein expression. Importantly, targeting IκBβ/NFκB signaling did not attenuate LPS-induced expression of anti-apoptotic genes or result in cell death. In endotoxemic neonatal mice, targeting LPS-induced IκBβ/NFκB signaling significantly attenuated pulmonary IL1β expression without affecting the anti-apoptotic gene expression.ConclusionTargeting IκBβ/NFκB signaling prevents LPS-induced IL1β expression without inducing apoptosis in cultured macrophages and in the lungs of endotoxemic newborn mice. Inhibiting this pathway may prevent inflammatory injury without affecting the protective role of NFκB activity in the developing lung.

LRRC25 Functions as an Inhibitor of NF-κB Signaling Pathway by Promoting p65/RelA for Autophagic Degradation

Nuclear factor κB (NF-κB) is a family of critical transcription factors that play a critical role in innate immune responses and inflammation, yet the molecular mechanisms responsible for its tight regulation is not fully understood. In this study, we identified LRRC25, a member of leucine-rich repeat (LRR)-containing protein family, as a negative regulator in the NF-κB signaling pathway. Ectopic expression of LRRC25 impaired NF-κB activation, whereas knockout of LRRC25 potentiated NF-κB activation and enhanced the production of inflammatory cytokines. Further study demonstrated that the LRR domain of LRRC25 interacted with the Rel Homology domain (RHD) of p65/RelA and promotes the degradation of p65/RelA. Furthermore, LRRC25 enhanced the interaction between p65/RelA and cargo receptor p62, thus facilitating the degradation of p65/RelA through autophagy pathway. Our study has not only identified LRRC25 as a novel inhibitor of NF-κB signaling pathway, but also uncovers a new mechanism of crosstalk between NF-κB signaling and autophagy pathways.

Effect of curcumin and paclitaxel on breast carcinogenesis

Global cancer burden increased to 14.1 million new cases in 2012; and breast cancer is the most common cancer in women worldwide, with nearly 1.7 million new cases diagnosed in 2012. Curcumin is the major bioactive ingredient extracted from the rhizome of the plant Curcuma longa (turmeric). Paclitaxel is a microtubule-stabilizing agent originally isolated from the bark of Taxus brevifolia. Curcumin and paclitaxel were evaluated with two human breast cancer cell lines as the luminal MCF-7 and the basal-like MDA-MB-231 that are either positive or negative for hormonal receptors estrogen receptor, progesterone receptor and HER2, respectively. Results indicated that curcumin combined with paclitaxel decreased c-Ha-Ras, Rho-A, p53 and Bcl-xL gene expression in comparison to control and substances alone in MCF-7 cell line. These two substances alone and combined decreased gene expression of Bcl-2 and NF-κB. However, CCND1 increased when both substances were combined in MCF-7 cells. Such substances decreased Bcl-2 and increased Bax protein expression. However, curcumin alone decreased IκBα and Stat-3 gene expression. Paclitaxel alone and combined increased IκBα and Stat-3. Curcumin alone and combined with paclitaxel increased p53, Bid, caspase-3, caspase-8 and Bax gene expression in MDA-MB-231, whereas Bcl-xL decreased such expression in MDA-MB-231 cells. When paclitaxel and curcumin were combined the expression of Bcl-2 protein was decreased. However, either substance alone and combined increased Bax protein expression corroborating the apoptotic effect of these substances. It can be concluded that curcumin may be of considerable value in synergistic therapy of breast cancer reducing the associated toxicity with use of drugs.

Anatomy of a negative feedback loop: the case of IκBα

The magnitude, duration and oscillation of cellular signalling pathway responses are often limited by negative feedback loops, defined as an 'activator-induced inhibitor' regulatory motif. Within the NFκB signalling pathway, a key negative feedback regulator is IκBα. We show here that, contrary to current understanding, NFκB-inducible expression is not sufficient for providing effective negative feedback. We then employ computational simulations of NFκB signalling to identify IκBα molecular properties that are critical for proper negative feedback control and test the resulting predictions in biochemical and single-cell live-imaging studies. We identified nuclear import and nuclear export of IκBα and the IκBα-NFκB complex, as well as the free IκBα half-life, as key determinants of post-induction repression of NFκB and the potential for subsequent reactivation. Our work emphasizes that negative feedback is an emergent systems property determined by multiple molecular and biophysical properties in addition to the required 'activator-induced inhibitor' relationship.

Endotoxemia Induces IκBβ/NF-κB-Dependent Endothelin-1 Expression in Hepatic Macrophages

Elevated serum concentrations of the vasoactive protein endothelin-1 (ET-1) occur in the setting of systemic inflammatory response syndrome and contribute to distal organ hypoperfusion and pulmonary hypertension. Thus, understanding the cellular source and transcriptional regulation of systemic inflammatory stress-induced ET-1 expression may reveal therapeutic targets. Using a murine model of LPS-induced septic shock, we demonstrate that the hepatic macrophage is the primary source of elevated circulating ET-1, rather than the endothelium as previously proposed. Using pharmacologic inhibitors, ET-1 promoter luciferase assays, and by silencing and overexpressing NF-κB inhibitory protein IκB expression, we demonstrate that LPS-induced ET-1 expression occurs via an NF-κB-dependent pathway. Finally, the specific role of the cRel/p65 inhibitory protein IκBβ was evaluated. Although cytoplasmic IκBβ inhibits activity of cRel-containing NF-κB dimers, nuclear IκBβ stabilizes NF-κB/DNA binding and enhances gene expression. Using targeted pharmacologic therapies to specifically prevent IκBβ/NF-κB signaling, as well as mice genetically modified to overexpress IκBβ, we show that nuclear IκBβ is both necessary and sufficient to drive LPS-induced ET-1 expression. Together, these results mechanistically link the innate immune response mediated by IκBβ/NF-κB to ET-1 expression and potentially reveal therapeutic targets for patients with Gram-negative septic shock.

Inhibiting IκBβ-NFκB signaling attenuates the expression of select pro-inflammatory genes

Multiple mediators of septic shock are regulated by the transcription factor nuclear factor κB (NFκB). However, complete NFκB inhibition can exacerbate disease, necessitating evaluation of targeted strategies to attenuate the pro-inflammatory response. Here, we demonstrate that in murine macrophages, low-dose NFκB inhibitors specifically attenuates lipopolysaccharide (LPS)-induced IκBβ degradation and the expression of a select subset of target genes (encoding IL1β, IL6, IL12β). Gain- and loss-of-function experiments demonstrate the necessary and sufficient role of inhibitor of NFκB family member IκBβ (also known as NFKBIB) in the expression of these genes. Furthermore, both fibroblasts and macrophages isolated from IκBβ overexpressing mice demonstrate attenuated LPS-induced IκBβ-NFκB signaling and IL1β, IL6 and IL12β expression. Further confirming the role of IκBβ and its NFκB subunit binding partner cRel in LPS-induced gene expression, pre-treatment of wild-type mouse embryonic fibroblasts with a cell-permeable peptide containing the cRel nuclear localization sequence attenuated IL6 expression. We prove that LPS-induced IκBβ-NFκB signaling can be selectively modulated to attenuate the expression of select pro-inflammatory target genes, thus providing therapeutic insights for patients exposed to systemic inflammatory stress.

IκBβ-mediated NF-κB activation confers protection against hyperoxic lung injury

Supplemental oxygen is frequently used in an attempt to improve oxygen delivery; however, prolonged exposure results in damage to the pulmonary endothelium and epithelium. Although NF-κB has been identified as a redox-responsive transcription factor, whether NF-κB activation exacerbates or attenuates hyperoxic lung injury is unclear. We determined that sustained NF-κB activity mediated by IκBβ attenuates lung injury and prevents mortality in adult mice exposed to greater than 95% O2. Adult wild-type mice demonstrated evidence of alveolar protein leak and 100% mortality by 6 days of hyperoxic exposure, and showed NF-κB nuclear translocation that terminated after 48 hours. Furthermore, these mice showed increased expression of NF-κB-regulated proinflammatory and proapoptotic cytokines. In contrast, mice overexpressing the NF-κB inhibitory protein, IκBβ (AKBI), demonstrated significant resistance to hyperoxic lung injury, with 50% surviving through 8 days of exposure. This was associated with NF-κB nuclear translocation that persisted through 96 hours of exposure. Although induction of NF-κB-regulated proinflammatory cytokines was not different between wild-type and AKBI mice, significant up-regulation of antiapoptotic proteins (BCL-2, BCL-XL) was found exclusively in AKBI mice. We conclude that sustained NF-κB activity mediated by IκBβ protects against hyperoxic lung injury through increased expression of antiapoptotic genes.

Sustained hyperoxia-induced NF-κB activation improves survival and preserves lung development in neonatal mice

Oxygen toxicity contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). Neonatal mice exposed to hyperoxia develop a simplified lung structure that resembles BPD. Sustained activation of the transcription factor NF-κB and increased expression of protective target genes attenuate hyperoxia-induced mortality in adults. However, the effect of enhancing hyperoxia-induced NF-κB activity on lung injury and development in neonatal animals is unknown. We performed this study to determine whether sustained NF-κB activation, mediated through IκBβ overexpression, preserves lung development in neonatal animals exposed to hyperoxia. Newborn wild-type (WT) and IκBβ-overexpressing (AKBI) mice were exposed to hyperoxia (>95%) or room air from day of life (DOL) 0-14, after which all animals were kept in room air. Survival curves were generated through DOL 14. Lung development was assessed using radial alveolar count (RAC) and mean linear intercept (MLI) at DOL 3 and 28 and pulmonary vessel density at DOL 28. Lung tissue was collected, and NF-κB activity was assessed using Western blot for IκB degradation and NF-κB nuclear translocation. WT mice demonstrated 80% mortality through 14 days of exposure. In contrast, AKBI mice demonstrated 60% survival. Decreased RAC, increased MLI, and pulmonary vessel density caused by hyperoxia in WT mice were significantly attenuated in AKBI mice. These findings were associated with early and sustained NF-κB activation and expression of cytoprotective target genes, including vascular endothelial growth factor receptor 2. We conclude that sustained hyperoxia-induced NF-κB activation improves neonatal survival and preserves lung development. Potentiating early NF-κB activity after hyperoxic exposure may represent a therapeutic intervention to prevent BPD.

NFκB function and regulation in cutaneous T-cell lymphoma

The nuclear accumulation and transcriptional activity of NFκB are constitutively increased in cutaneous T-cell lymphoma (CTCL) cells, and are responsible for their increased survival and proliferation. However, in addition to the anti-apoptotic and pro-inflammatory genes, NFκB induces expression of immunosuppressive genes, such as IL-10 and TGFβ, which inhibit the immune responses and are characteristic for the advanced stages of CTCL. While the mechanisms regulating NFκB-dependent transcription of anti-apoptotic and pro-inflammatory genes have been studied extensively, very little is known about the NFκB regulation of immunosuppressive genes. The specificity of NFκB-regulated responses is determined by the subunit composition of NFκB complexes recruited to the individual promoters, post-translational modifications of NFκB proteins, as well as by their interactions with other transcriptional factors and regulators. In this review, we discuss the mechanisms regulating the transcription of NFκB-dependent anti-apoptotic, pro-inflammatory and immunosuppressive genes in CTCL cells, as potential targets for CTCL therapies.

Chromatin-bound IκBα regulates a subset of polycomb target genes in differentiation and cancer

IκB proteins are the primary inhibitors of NF-κB. Here, we demonstrate that sumoylated and phosphorylated IκBα accumulates in the nucleus of keratinocytes and interacts with histones H2A and H4 at the regulatory region of HOX and IRX genes. Chromatin-bound IκBα modulates Polycomb recruitment and imparts their competence to be activated by TNFα. Mutations in the Drosophila IκBα gene cactus enhance the homeotic phenotype of Polycomb mutants, which is not counteracted by mutations in dorsal/NF-κB. Oncogenic transformation of keratinocytes results in cytoplasmic IκBα translocation associated with a massive activation of Hox. Accumulation of cytoplasmic IκBα was found in squamous cell carcinoma (SCC) associated with IKK activation and HOX upregulation.

Evolutionary, structural and functional interplay of the IκB family members

A primary level of control for nuclear factor kappa B (NF-κB) is effected through its interactions with the inhibitor protein, inhibitor of kappa B (IκB). Several lines of evidence confirm the existence of multiple forms of IκB that appear to regulate NF-κB by distinct mechanisms. Therefore, we performed a comprehensive bioinformatics analysis to understand the evolutionary history and intrinsic functional diversity of IκB family members. Phylogenetic relationships were constructed to trace the evolution of the IκB family genes. Our phylogenetic analysis revealed 10 IκB subfamily members that clustered into 5 major clades. Since the ankyrin (ANK) domain appears to be more ancient than the Rel homology domain (RHD), our phylogenetic analysis suggests that some undefined ancestral set of ANK repeats acquired an RHD before any duplication and was later duplicated and then diverged into the different IκB subfamilies. Functional analysis identified several functionally divergent sites in the ANK repeat domains (ARDs) and revealed that this region has undergone strong purifying selection, suggesting its functional importance in IκB genes. Structural analysis showed that the major variations in the number of ANK repeats and high conformational changes in the finger loop ARD region contribute to the differing binding partner specificities, thereby leading to distinct IκB functions. In summary, our study has provided useful information about the phylogeny and structural and functional divergence of the IκB family. Additionally, we identified a number of amino acid sites that contribute to the predicted functional divergence of these proteins.

It takes two to tango: IκBs, the multifunctional partners of NF-κB

The inhibitory IκB proteins have been discovered as fundamental regulators of the inducible transcription factor nuclear factor-κB (NF-κB). As a generally excepted model, stimulus-dependent destruction of inhibitory IκBs and processing of precursor molecules, both promoted by components of the signal integrating IκB kinase complex, are the key events for the release of various NF-κB/Rel dimers and subsequent transcriptional activation. Intense research of more than 20 years provides evidence that the extending family of IκBs act not simply as reversible inhibitors of NF-κB activation but rather as a complex regulatory module, which assures feedback regulation of the NF-κB system and either can inhibit or promote transcriptional activity in a stimulus-dependent manner. Thus, IκB and NF-κB/Rel family proteins establish a complex interrelationship that allows modulated NF-κB-dependent transcription, tailored to the physiological environment.

Regulation of NF-κB by ubiquitination and degradation of the IκBs

The nuclear factor-κB (NF-κB) signaling pathway is a busy ground for the action of the ubiquitin-proteasome system; many of the signaling steps are coordinated by protein ubiquitination. The end point of this pathway is to induce transcription, and to this end, there is a need to overcome a major obstacle, a set of inhibitors (IκBs) that bind NF-κB and prohibit either the nuclear entry or the DNA binding of the transcription factor. Two major signaling steps are required for the elimination of the inhibitors: activation of the IκB kinase (IKK) and degradation of the phosphorylated inhibitors. IKK activation and IκB degradation involve different ubiquitination modes; the latter is mediated by a specific E3 ubiquitin ligase SCF(β-TrCP) . The F-box component of this E3, β-TrCP, recognizes the IκB degron formed following phosphorylation by IKK and thus couples IκB phosphorylation to ubiquitination. SCF(β-TrCP) -mediated IκB ubiquitination and degradation is a very efficient process, often resulting in complete degradation of the key inhibitor IκBα within a few minutes of cell stimulation. In vivo ablation of β-TrCP results in accumulation of all the IκBs and complete NF-κB inhibition. As many details of IκB-β-TrCP interaction have been worked out, the development of β-TrCP inhibitors might be a feasible therapeutic approach for NF-κB-associated human disease. However, we may still need to advance our understanding of the mechanism of IκB degradation as well as of the diverse functions of β-TrCP in vivo.

NF-κB, the first quarter-century: remarkable progress and outstanding questions

The ability to sense and adjust to the environment is crucial to life. For multicellular organisms, the ability to respond to external changes is essential not only for survival but also for normal development and physiology. Although signaling events can directly modify cellular function, typically signaling acts to alter transcriptional responses to generate both transient and sustained changes. Rapid, but transient, changes in gene expression are mediated by inducible transcription factors such as NF-κB. For the past 25 years, NF-κB has served as a paradigm for inducible transcription factors and has provided numerous insights into how signaling events influence gene expression and physiology. Since its discovery as a regulator of expression of the κ light chain gene in B cells, research on NF-κB continues to yield new insights into fundamental cellular processes. Advances in understanding the mechanisms that regulate NF-κB have been accompanied by progress in elucidating the biological significance of this transcription factor in various physiological processes. NF-κB likely plays the most prominent role in the development and function of the immune system and, not surprisingly, when dysregulated, contributes to the pathophysiology of inflammatory disease. As our appreciation of the fundamental role of inflammation in disease pathogenesis has increased, so too has the importance of NF-κB as a key regulatory molecule gained progressively greater significance. However, despite the tremendous progress that has been made in understanding the regulation of NF-κB, there is much that remains to be understood. In this review, we highlight both the progress that has been made and the fundamental questions that remain unanswered after 25 years of study.

Signaling by the tumor necrosis factor receptor superfamily in B-cell biology and disease

Members of the tumor necrosis factor receptor superfamily (TNFRSF) participate prominently in B-cell maturation and function. In particular, B-cell activating factor belonging to the TNF family receptor (BAFF-R), B-cell maturation antigen (BCMA), and transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) play critical roles in promoting B-cell survival at distinct stages of development by engaging a proliferation-inducing ligand (APRIL) and/or BAFF. CD40 is also essential for directing the humoral response to T-cell-dependent antigens. Signaling by the TNFRSF is mediated primarily, albeit not exclusively, via the TNFR-associated factor (TRAF) proteins and activation of the canonical and/or non-canonical nuclear factor-κB (NF-κB) pathways. Dysregulated signaling by TNFRSF members can promote B-cell survival and proliferation, causing autoimmunity and neoplasia. In this review, we present a current understanding of the functions of and distinctions between APRIL/BAFF signaling by their respective receptors expressed on particular B-cell subsets. These findings are compared and contrasted with CD40 signaling, which employs similar signaling conduits to achieve distinct cellular outcomes in the context of the germinal center response. We also underscore how new findings and conceptual insights into TNFRSF signaling are facilitating the understanding of B-cell malignancies and autoimmune diseases.

Nuclear factor-κB (NF-κB) inhibitory protein IκBβ determines apoptotic cell death following exposure to oxidative stress

The transcription factor NF-κB regulates the cellular response to inflammatory and oxidant stress. Although many studies have evaluated NF-κB activity following exposure to oxidative stress, the role of the IκB family of inhibitory proteins in modulating this activity remains unclear. Specifically, the function of IκBβ in mediating the cellular response to oxidative stress has not been evaluated. We hypothesized that blocking oxidative stress-induced NF-κB signaling through IκBβ would prevent apoptotic cell death. Using IκBβ knock-in mice (AKBI), in which the IκBα gene is replaced with the IκBβ cDNA, we show that IκBβ overexpression prevented oxidative stress-induced apoptotic cell death. This was associated with retention of NF-κB subunits in the nucleus and maintenance of NF-κB activity. Furthermore, the up-regulation of pro-apoptotic genes in WT murine embryonic fibroblasts (MEFs) exposed to serum starvation was abrogated in AKBI MEFs. Inhibition of apoptosis was observed in WT MEFs overexpressing IκBβ with simultaneous IκBα knockdown, whereas IκBβ overexpression alone did not produce this effect. These findings represent a necessary but not sufficient role of IκBβ in preventing oxidant stress-induced cell death.

IκBβ attenuates angiotensin II-induced cardiovascular inflammation and fibrosis in mice

The development of cardiovascular fibrosis is associated with chronic inflammation, where activation of nuclear factor κB (NF-κB) signaling may play a critical role. NF-κB activation is tightly regulated by the cellular inhibitor of κB (IκB) family of proteins, such as IκBα and IκBβ. IκBα and IκBβ display different regulation kinetics in response to inflammatory stimulation. The present study tested the hypothesis that IκBα and IκBβ may have different roles in modulating cardiovascular inflammation and fibrosis, using a model of angiotensin II infusion-induced hypertension in wild-type mice and IκBβ knock-in mice, in which the IκBα gene is replaced by IκBβ cDNA (AKBI). In WT mice, subcutaneous angiotensin II infusion for 7 days induced increased perivascular and interstitial collagen deposition and fibrotic lesions, associated with myocardial interstitial hemosiderin accumulation and extensive macrophage infiltration. These effects of angiotensin II were dramatically limited in AKBI mice. Replacement of IκBα with IκBβ significantly attenuated angiotensin II infusion-induced expression of interleukin 1β, interleukin 6, monocyte chemotactic protein 1, collagen I and III, fibronectin, and tissue inhibitor of metalloproteinase 1 in the hearts. Furthermore, using cultured vascular smooth muscle cells, we demonstrated that interleukin 1β-induced NF-κB activation and monocyte chemotactic protein 1, vascular cell adhesion molecule 1, and tissue inhibitor of metalloproteinase 1 expressions were suppressed in the AKBI cells because of the replacement of IκBα with IκBβ. These results indicate that NF-κB has an essential role in mediating the cardiovascular inflammatory response to angiotensin II and suggest that targeting the balance of IκBα and IκBβ expression might be a novel therapeutic modality in preventing fibrosis in hypertensive cardiovascular disease.

p65 controls NF-κB activity by regulating cellular localization of IκBβ

NF-κB (nuclear factor κB) controls diverse cellular processes and is frequently misregulated in chronic immune diseases or cancer. The activity of NF-κB is regulated by IκB (inhibitory κB) proteins which control nuclear-cytoplasmic shuttling and DNA binding of NF-κB. In the present paper, we describe a novel role for p65 as a critical regulator of the cellular localization and functions of NF-κB and its inhibitor IκBβ. In genetically modified p65-/- cells, the localization of ectopic p65 is not solely regulated by IκBα, but is largely dependent on the NLS (nuclear localization signal) and the NES (nuclear export signal) of p65. Furthermore, unlike IκBα, IκBβ does not contribute to the nuclear export of p65. In fact, the cellular localization and degradation of IκBβ is controlled by the p65-specific NLS and NES. The results of our present study also reveal that, in addition to stimulus-induced redistribution of NF-κB, changes in the constitutive localization of p65 and IκBβ specifically modulate activation of inflammatory genes. This is a consequence of differences in the DNA-binding activity and signal responsiveness between the nuclear and cytoplasmic NF-κB-IκBβ complexes. Taken together, the findings of the present study indicate that the p65 subunit controls transcriptional competence of NF-κB by regulating the NF-κB/IκBβ pathway.

Alternative nuclear functions for NF-κB family members

The NF-κB signalling pathway regulates many different biological processes from the cellular level to the whole organism. The majority of these functions are completely dependent on the activation of the cytoplasmic IKK kinase complex that leads to IκB degradation and results in the nuclear translocation of specific NF-κB dimers, which, in general, act as transcription factors. Although this is a well-established mechanism of action, several publications have now demonstrated that some members of this pathway display additional functions in the nucleus as regulators of NF-κB-dependent and independent gene expression. In this review, we compiled and put in context most of the data concerning specific nuclear roles for IKK and IκB proteins.

The NF-kappaB family of transcription factors and its regulation

Nuclear factor-kappaB (NF-kappaB) consists of a family of transcription factors that play critical roles in inflammation, immunity, cell proliferation, differentiation, and survival. Inducible NF-kappaB activation depends on phosphorylation-induced proteosomal degradation of the inhibitor of NF-kappaB proteins (IkappaBs), which retain inactive NF-kappaB dimers in the cytosol in unstimulated cells. The majority of the diverse signaling pathways that lead to NF-kappaB activation converge on the IkappaB kinase (IKK) complex, which is responsible for IkappaB phosphorylation and is essential for signal transduction to NF-kappaB. Additional regulation of NF-kappaB activity is achieved through various post-translational modifications of the core components of the NF-kappaB signaling pathways. In addition to cytosolic modifications of IKK and IkappaB proteins, as well as other pathway-specific mediators, the transcription factors are themselves extensively modified. Tremendous progress has been made over the last two decades in unraveling the elaborate regulatory networks that control the NF-kappaB response. This has made the NF-kappaB pathway a paradigm for understanding general principles of signal transduction and gene regulation.

Ubiquitination and degradation of the inhibitors of NF-kappaB

The key step in NF-kappaB activation is the release of the NF-kappaB dimers from their inhibitory proteins, achieved via proteolysis of the IkappaBs. This irreversible signaling step constitutes a commitment to transcriptional activation. The signal is eventually terminated through nuclear expulsion of NF-kappaB, the outcome of a negative feedback loop based on IkappaBalpha transcription, synthesis, and IkappaBalpha-dependent nuclear export of NF-kappaB (Karin and Ben-Neriah 2000). Here, we review the process of signal-induced IkappaB ubiquitination and degradation by comparing the degradation of several IkappaBs and discussing the characteristics of IkappaBs' ubiquitin machinery.

NF-κB and STAT3 signaling hubs for lung innate immunity

Innate immune responses to lung pathogens involve the coordinated expression of myriad affector and effector molecules of innate immunity, which must be induced and appropriately regulated in response to diverse stimuli generated by microbes or the infected host. Many intercellular and intracellular signaling pathways are involved, but we propose NF-κB and STAT3 transcription factors to be especially important signaling hubs for integrating these pathways to orchestrate effective host defense without excessive inflammatory injury.

IkappaBbeta acts to inhibit and activate gene expression during the inflammatory response

The activation of pro-inflammatory gene programs by nuclear factor-kappaB (NF-kappaB) is primarily regulated through cytoplasmic sequestration of NF-kappaB by the inhibitor of kappaB (IkappaB) family of proteins. IkappaBbeta, a major isoform of IkappaB, can sequester NF-kappaB in the cytoplasm, although its biological role remains unclear. Although cells lacking IkappaBbeta have been reported, in vivo studies have been limited and suggested redundancy between IkappaBalpha and IkappaBbeta. Like IkappaBalpha, IkappaBbeta is also inducibly degraded; however, upon stimulation by lipopolysaccharide (LPS), it is degraded slowly and re-synthesized as a hypophosphorylated form that can be detected in the nucleus. The crystal structure of IkappaBbeta bound to p65 suggested this complex might bind DNA. In vitro, hypophosphorylated IkappaBbeta can bind DNA with p65 and c-Rel, and the DNA-bound NF-kappaB:IkappaBbeta complexes are resistant to IkappaBalpha, suggesting hypophosphorylated, nuclear IkappaBbeta may prolong the expression of certain genes. Here we report that in vivo IkappaBbeta serves both to inhibit and facilitate the inflammatory response. IkappaBbeta degradation releases NF-kappaB dimers which upregulate pro-inflammatory target genes such as tumour necrosis factor-alpha (TNF-alpha). Surprisingly, absence of IkappaBbeta results in a dramatic reduction of TNF-alpha in response to LPS even though activation of NF-kappaB is normal. The inhibition of TNF-alpha messenger RNA (mRNA) expression correlates with the absence of nuclear, hypophosphorylated-IkappaBbeta bound to p65:c-Rel heterodimers at a specific kappaB site on the TNF-alpha promoter. Therefore IkappaBbeta acts through p65:c-Rel dimers to maintain prolonged expression of TNF-alpha. As a result, IkappaBbeta(-/-) mice are resistant to LPS-induced septic shock and collagen-induced arthritis. Blocking IkappaBbeta might be a promising new strategy for selectively inhibiting the chronic phase of TNF-alpha production during the inflammatory response.

Defective feedback regulation of NF-kappaB underlies Sjogren's syndrome in mice with mutated kappaB enhancers of the IkappaBalpha promoter

Feedback regulation of transcription factor NF-kappaB by its inhibitor IkappaBalpha plays an essential role in control of NF-kappaB activity. To understand the biological significance of IkappaBalpha-mediated feedback regulation of NF-kappaB, we generated mice harboring mutated kappaB enhancers in the promoter of the IkappaBalpha gene (IkappaBalpha(M/M)) to inhibit NF-kappaB-regulated IkappaBalpha expression. Here, we report that these mutant mice are defective in NF-kappaB-induced expression of IkappaBalpha. This defective feedback regulation of NF-kappaB by IkappaBalpha not only altered activity of NF-kappaB, but also the expression of NF-kappaB-regulated genes. As a result, IkappaBalpha(M/M), the homozygous knock-in mice with mutated kappaB enhancers in the IkappaBalpha promoter, acquire shorten life span, hypersensitivity to septic shock, abnormal T-cell development and activation, and Sjögren's Syndrome. These findings therefore demonstrate that the IkappaBalpha-mediated feedback regulation of NF-kappaB has an essential role in controlling T-cell development and functions, provide mechanistic insight into the development of Sjögren's Syndrome, and suggest the potential of NF-kappaB signaling as a therapeutic target for Sjögren's Syndrome and other autoimmune diseases.

Searching for NF-kappaB-based treatments of ischemia reperfusion injury

When a tissue becomes ischemic, a host of changes occur at the cellular level that lead to a shift in transcriptional activity of many inflammatory and cytoprotective compounds, a process which is extensively controlled through a family of transcription factors known as nuclear factor kappa-B (NF-kappaB). This shift in activity paradoxically results in both a cytoprotective effect at the cellular level and upon reperfusion, a generally destructive inflammatory response, a phenomenon referred to as ischemia reperfusion (IR) injury. To date, a number of methods of modifying the activity of NF-kappaB through either physiologic or pharmacologic manipulation have been developed and studied in animal models of IR injury and in some cases in human clinical trials. Nearly every method of NF-kappaB antagonism has demonstrated a discrete protective effect allowing investigators to reduce myocardial infarct sizes by 60% and cerebral infarct sizes by 57% relative to untreated control animals. The problem of IR injury is all too common and represents a discrete threat not only to the tissues directly involved in the ischemic event, but also to distal sites as well as is seen in the evolution of acute respiratory distress and severe inflammatory response syndromes. In the course of this review, the nature of NF-kappaB and its involvement in IR injury is examined along with the efficacy of the various NF-kappaB-based investigational treatment developed to date.

Autoregulatory feedback loops terminating the NF-kappaB response

After nuclear factor (NF)-kappaB activation, a complex network of negative feedback loops ensures that the termination of the NF-kappaB response occurs in a highly organized manner. Recent results show that signals initiated during the induction phase already program a default termination procedure that enables temporally and spatially regulated NF-kappaB deactivation. All negative feedback mechanisms occur with a characteristic time delay, thereby permitting full NF-kappaB function during the interim period. Some proteins that direct termination are produced directly in response to NF-kappaB activation, whereas others are activated via inducible binding or by protein stabilization. Another time-delaying strategy of NF-kappaB feedback inhibitory proteins relies on their ability to function as timers and molecular clockworks with the intrinsic property to terminate their own activity within a preset period.

A new regulatory mechanism of NF-kappaB activation by I-kappaBbeta in cancer cells

Transglutaminase 2 (TGase 2) catalyzes covalent isopeptide bond formation between glutamine and lysine residues. Recently, we reported that TGase 2 activates nuclear factor-kappa B (NF-kappaB) by depleting inhibitor of NF-kappaBalpha (I-kappaBalpha) levels via polymer formation. Furthermore, TGase 2 expression synergistically increases NF-kappaB activity with canonical pathway. The major I-kappaB proteins such as I-kappaBalpha and I-kappaBbeta resemble each other in both primary sequence and tertiary structure. However, I-kappaBbeta does not degrade fully, while I-kappaBalpha degrades immediately in response to most stimuli. We found that I-kappaBbeta does not contain any of the previously identified TGase 2 target sites. In this study, both an in vitro cross-linking assay and a TGase 2 transfection assay revealed that I-kappaBbeta is independent from TGase 2-mediated polymerization. Furthermore, increased I-kappaBbeta expression reversed NF-kappaB activation in cancer cells, compensating for the loss of I-kappaBalpha via TGase 2 polymerization.

The phylogeny of the mammalian heme peroxidases and the evolution of their diverse functions

BACKGROUND

The mammalian heme peroxidases (MHPs) are a medically important group of enzymes. Included in this group are myeloperoxidase, eosinophil peroxidase, lactoperoxidase, and thyroid peroxidase. These enzymes are associated with such diverse diseases as asthma, Alzheimer's disease and inflammatory vascular disease. Despite much effort to elucidate a clearer understanding of the function of the 4 major groups of this multigene family, we still do not have a clear understanding of their relationships to each other.

RESULTS

Sufficient signal exists for the resolution of the evolutionary relationships of this family of enzymes. We demonstrate, using a root mean squared deviation statistic, how the removal of the fastest evolving sites aids in the minimisation of the effect of long branch attraction and the generation of a highly supported phylogeny. Based on this phylogeny we have pinpointed the amino acid positions that have most likely contributed to the diverse functions of these enzymes. Many of these residues are in close proximity to sites implicated in protein misfolding, loss of function or disease.

CONCLUSION

Our analysis of all available genomic sequence data for the MHPs from all available completed mammalian genomes, involved sophisticated methods of phylogeny reconstruction and data treatment. Our study has (i) fully resolved the phylogeny of the MHPs and the subsequent pattern of gene duplication, and (ii), we have detected amino acids under positive selection that have most likely contributed to the observed functional shifts in each type of MHP.

Shared principles in NF-kappaB signaling

The transcription factor NF-kappaB has served as a standard for inducible transcription factors for more than 20 years. The numerous stimuli that activate NF-kappaB, and the large number of genes regulated by NF-kappaB, ensure that this transcription factor is still the subject of intense research. Here, we attempt to synthesize some of the basic principles that have emerged from studies of NF-kappaB, and we aim to generate a more unified view of NF-kappaB regulation.

Surfactant protein A activation of atypical protein kinase C zeta in IkappaB-alpha-dependent anti-inflammatory immune regulation

The pulmonary collectin surfactant protein (SP)-A has a pivotal role in anti-inflammatory modulation of lung immunity. The mechanisms underlying SP-A-mediated inhibition of LPS-induced NF-kappaB activation in vivo and in vitro are only partially understood. We previously demonstrated that SP-A stabilizes IkappaB-alpha, the primary regulator of NF-kappaB, in alveolar macrophages (AM) both constitutively and in the presence of LPS. In this study, we show that in AM and PBMC from IkappaB-alpha knockout/IkappaB-beta knockin mice, SP-A fails to inhibit LPS-induced TNF-alpha production and p65 nuclear translocation, confirming a critical role for IkappaB-alpha in SP-A-mediated LPS inhibition. We identify atypical (a) protein kinase C (PKC) zeta as a pivotal upstream regulator of SP-A-mediated IkappaB-alpha/NF-kappaB pathway modulation deduced from blocking experiments and confirmed by using AM from PKCzeta-/- mice. SP-A transiently triggers aPKCThr(410/403) phosphorylation, aPKC kinase activity, and translocation in primary rat AM. Coimmunoprecipitation experiments reveal that SP-A induces aPKC/p65 binding under constitutive conditions. Together the data indicate that anti-inflammatory macrophage activation via IkappaB-alpha by SP-A critically depends on PKCzeta activity, and thus attribute a novel, stimulus-specific signaling function to PKCzeta in SP-A-modulated pulmonary immune response.

Hepatic tumor necrosis factor signaling and nuclear factor-kappaB: effects on liver homeostasis and beyond

The proinflammatory cytokine TNF has a pivotal role in liver pathophysiology because it holds the capacity to induce both hepatocyte cell death and hepatocyte proliferation. This dual effect of TNF on hepatocytes reflects its ability to induce both nuclear factor kappaB (NF-kappaB)-dependent gene expression and cell death. Multiple studies have demonstrated the crucial role of the transcription factor NF-kappaB in the decision between life and death of a hepatocyte. Massive hepatocyte apoptosis preceding embryonic lethality in NF-kappaB-deficient mice constituted the first indication of an essential antiapoptotic function of NF-kappaB in the liver. Although many studies confirmed this crucial cytoprotective role of NF-kappaB in adult liver, a number of genetic studies recently obtained conflicting results on the exact role of NF-kappaB in different mouse models of TNF hepatotoxicity, demonstrating that caution should be taken when interpreting studies using different NF-kappaB-deficient mice in distinct models of liver injury. Recent reports showing a role for hepatic NF-kappaB activation in the proliferation of malignant cells during hepatocarcinogenesis, and in the progression of fatty liver diseases to insulin resistance and type 2 diabetes mellitus demonstrate that NF-kappaB can also have more detrimental effects in the liver. Moreover, its role in the development of the metabolic syndrome emphasizes that hepatic NF-kappaB activation might also have adverse effects on the endocrine system. Therefore, understanding the regulation of hepatic TNF signaling and NF-kappaB activation is of critical therapeutic importance. In this review, we summarize how studies on the role of NF-kappaB in different mouse models of liver pathologies have contributed to this understanding.

IkappaBalpha independent induction of NF-kappaB and its inhibition by DHMEQ in Hodgkin/Reed-Sternberg cells

Constitutive nuclear factor kappaB (NF-kappaB) activation characterizes Hodgkin/Reed-Sternberg (H-RS) cells. Blocking constitutive NF-kappaB has been shown to be a potential strategy to treat Hodgkin lymphoma (HL). Here, for the first time we show that although constitutive NF-kappaB level of H-RS cell lines is very high, topoisomerase inhibitors further enhance NF-kappaB activation through IkappaB kinase activation in not only H-RS cell lines with wild-type IkappaBalpha, but also in those with IkappaBalpha mutations and lacking wild-type IkappaBalpha. Thus, both constitutive and inducible NF-kappaB are potential targets to treat HL. We also present the data that indicate the involvement of IkappaBbeta in NF-kappaB induction by topoisomerase inhibitors. A new NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ) inhibited constitutive NF-kappaB activity and induced apoptosis of H-RS cell lines. DHMEQ also inhibited the growth of H-RS cells without significant systemic toxicity in a NOD/SCID/gammac(null) (NOG) mice model. DHMEQ and topoisomerase inhibitors revealed enhancement of apoptosis of H-RS cells by blocking inducible NF-kappaB. Results of this study suggest that both constitutive and inducible NF-kappaB are molecular targets of DHMEQ in the treatment of HL. The results also indicate that IkappaBbeta is involved in NF-kappaB activation in H-RS cells and IkappaBbeta substitutes for IkappaBalpha in H-RS cells lacking wild-type IkappaBalpha.

Induced fit, folding, and recognition of the NF-kappaB-nuclear localization signals by IkappaBalpha and IkappaBbeta

Protein structure prediction codes based on the associative memory Hamiltonian were used to probe the binding modes between the nuclear localization signal (NLS) polypeptide of NF-kappaB and the inhibitors IkappaBalpha and IkappaBbeta. Experimentally, it is known that the NLS polypeptide is unstructured in the NF-kappaB complex with DNA but it forms an extended helical structure with the NLS (residues 301-304) between the two helices in the NF-kappaB/IkappaBalpha complex. The simulations included the NF-kappaB(p65) and (p50) NLS polypeptides and various mutants alone and in the presence of IkappaBalpha and IkappaBbeta. The simulations predict that the NLS polypeptide by itself binds tightly to IkappaBalpha and IkappaBbeta. In the NF-kappaB (p50/p65) heterodimer, the p50 NLS is predicted to remain free to bind to importin alpha. In the interaction with IkappaBalpha, both p65 NLSs are predicted to be bound. In IkappaBbeta, the NLS polypeptide binds to two binding sites, as seen in the crystal structure, with one site heavily favored for stable binding.

In vivo binding of NF-kappaB to the IkappaBbeta promoter is insufficient for transcriptional activation

Despite certain structural and biochemical similarities, differences exist in the function of the NF-kappaB (nuclear factor kappaB) inhibitory proteins IkappaBalpha (inhibitory kappaBalpha) and IkappaBbeta. The functional disparity arises in part from variance at the level of gene regulation, and in particular from the substantial induction of IkappaBalpha, but not IkappaBbeta, gene expression post-NF-kappaB activation. In the present study, we probe the differential effects of IL (interleukin)-1beta on induction of IkappaBalpha and perform the first characterization of the human IkappaBbeta promoter. A consensus NF-kappaB-binding site, capable of binding NF-kappaB both in vitro and in vivo, is found in the IkappaBbeta gene 5' flanking region. However, the IkappaBbeta promoter was not substantially activated by pro-inflammatory cytokines, such as IL-1beta and tumour necrosis factor alpha, that are known to cause strong activation of NF-kappaB. Furthermore, in contrast with IkappaBalpha, NF-kappaB activation did not increase expression of endogenous IkappaBbeta as assessed by analysis of mRNA and protein levels. Unlike kappaB-responsive promoters, IkappaBbeta promoter-bound p65 inefficiently recruits RNA polymerase II, which stalls at the promoter. We present evidence that this stalling is likely due to the absence of transcription factor IIH engagement, a prerequisite for RNA polymerase II phosphorylation and transcriptional initiation. Differences in the conformation of promoter-bound NF-kappaB may underlie the variation in the ability to engage the basal transcriptional apparatus at the IkappaBbeta and kappaB-responsive promoters. This accounts for the differential expression of IkappaB family members in response to NF-kappaB activation and furthers our understanding of the mechanisms involved in transcription factor activity and IkappaBbeta gene regulation.

Effects of melatonin and age on gene expression in mouse CNS using microarray analysis

The expression levels of a number of genes associated with inflammation and immune function change with advancing age. Melatonin modulates gene expression levels of several of these genes. Therefore the declining levels of melatonin associated with age may play a role in the physiological effects of aging. We used oligonucleotide microarrays to measure age-related changes in mRNA expression in the murine CNS, and to study the effect of prolonged administration of dietary melatonin upon these changes. CB6F1 male mice were fed 40 ppm melatonin for 2.1 months prior to sacrifice at age 26.5 months, and compared with both age-matched controls and young, 4.5-month-old untreated controls. Total RNA was extracted from whole brain (excluding cerebellum and brain stem) and individual samples were hybridized to Affymetrix Mouse 430-2.0 arrays. The expression of a substantial number of genes was modulated by melatonin treatment and changes in selected genes were validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). A subset of these genes did not change with age. Conversely, some genes modulated by age were also modulated by melatonin treatment. In general, melatonin treatment drove the expression levels of these genes closer to the expression levels detected in the younger animals. Notably, the abundance of lipocalin 2 (Lcn2) mRNA increased with age and was decreased in old animals treated with melatonin. Lcn2 is a member of the acute phase response family of proteins and its mRNA levels in the brain increase in response to inflammation. Many of the genes with expression reduced by melatonin are involved in inflammation and the immune system. This suggests that melatonin treatment may influence the inflammatory responses of old animals, driving them to resemble more closely those occurring in young animals.

Unravelling the complexities of the NF-κB signalling pathway using mouse knockout and transgenic models

The nuclear factor-kappaB (NF-kappaB) signalling pathway serves a crucial role in regulating the transcriptional responses of physiological processes that include cell division, cell survival, differentiation, immunity and inflammation. Here we outline studies using mouse models in which the core components of the NF-kappaB pathway, namely the IkappaB kinase subunits (IKKalpha, IKKbeta and NEMO), the IkappaB proteins (IkappaBalpha, IkappaBbeta, IkappaBvarepsilon and Bcl-3) and the five NF-kappaB transcription factors (NF-kappaB1, NF-kappaB2, c-Rel, RelA and RelB), have been genetically manipulated using transgenic and knockout technology.

Dissection of the NF-kappaB signalling cascade in transgenic and knockout mice

Studies in transgenic and knockout mice have made a major contribution to our current understanding of the physiological functions of the NF-kappaB signalling cascade. The generation and analysis of mice with targeted modifications of individual components of the NF-kappaB pathway tremendously advanced our knowledge of the roles of the NF-kappaB proteins themselves, and also of the many activators and negative regulators of NF-kappaB. These studies have highlighted the complexity of the NF-kappaB system, by revealing the multiple interactions, redundancies, but also diverse functions, performed by the different molecules participating in the regulation of NF-kappaB signalling. Furthermore, inhibition or enforced activation of NF-kappaB in transgenic mice has uncovered the critical roles that NF-kappaB plays in the pathogenesis of various diseases such as liver failure, diabetes and cancer.